1. Field of the Invention
The invention relates to amorphous metal alloy compositions and, in particular, to amorphous alloys containing iron, silicon and boron having enhanced AC magnetic properties at elevated temperatures.
2. Description of the Prior Art
Investigations have demonstrated that it is possible to obtain solid amorphous materials from certain metal alloy compositions. An amorphous material substantially lacks any long range atomic order and is characterized by an X-ray diffraction profile consisting of broad intensity maxima. Such a profile is qualitatively similar to the diffraction profile of a liquid or ordinary window glass. This is in contrast to a crystalline material which produces a diffraction profile consisting of sharp, narrow intensity maxima.
These amorphous materials exist in a metastable state. Upon heating to a sufficiently high temperature, they crystallize with evolution of the heat of crystallization, and the X-ray diffraction profile changes from one having amorphous characteristics to one having crystalline characteristics.
Novel amorphous metal alloys have been disclosed by H. S. Chen and D. E. Polk in U.S. Pat. No. 3,856,513, issued Dec. 24, 1974. These amorphous alloys have the formula M.sub.a Y.sub.b Z.sub.c where M is at least one metal selected from the group of iron, nickel, cobalt, chromium and vanadium, Y is at least one element selected from the group consisting of phosphorus, boron and carbon, Z is at least one element selected from the group consisting of aluminum, antimony, beryllium, germanium, indium, tin and silicon, "a" ranges from about 60 to 90 atom percent, "b" ranges from about 10 to 30 atom percent and "c" ranges from about 0.1 to 15 atom percent. These amorphous alloys have been found suitable for a wide variety of applications in the form of ribbon, sheet, wire, powder, etc. The Chen and Polk patent also discloses, amorphous alloys having the formula T.sub.i X.sub.j, where T is at least one transition metal, X is at least one element selected from the group consisting of aluminum, antimony, beryllium, boron, germanium, carbon, indium, phosphorus, silicon and tin, "i" ranges from about 70 to 87 atom percent and "j" ranges from about 13 to 30 atom percent. These amorphous alloys have been found suitable for wire applications.
U.S. Pat. No. 4,300,950 discloses amorphous metal alloys consisting essentially of 12 to 15% boron, 1 to 8% silicon and 80 to 84% iron, by atomic percentage. These alloys exhibit relatively low crystallization and curie temperatures (i.e. less than 400.degree. C.). As a result, the magnetic properties thereof are substantially degraded by long term thermal aging, and the induction levels of the alloys are relatively low at elevated temperatures. Hence, the alloys are not well suited for power magnetics applications wherein operating temperatures frequently exceed 100.degree. C.
European Patent Application 095,831, filed Mar. 28, 1983 discloses amorphous metal alloys consisting of 4-10% boron, 14-17% silicon and 73-80% iron, by atomic percentages and incidental impurities. These alloys evidence high exciting power (e.g. of the order of 3-5 VA/kg at 60 Hz and 1.4 T) and are not well suited for power magnetics appliations wherein low exciting power is required.
European Patent Application 095,803, filed Mar. 28, 1983 discloses amorphous metal alloys consisting of 6-10% boron, 14-17% silicon and 1-4% chromium, by atomic percentages, no more than incidental impurities and the balance iron. These chromium containing alloys have relatively low intrinsic saturation induction and relatively low curie temperature, and are unsuitable for elevated temperature, high induction applications.
U.S. Pat. No. 4,437,907 discloses amorphous metal alloys composed of 8-19% silicon, 6-13% boron 0-3.5 carbon and 74-80% iron, by atomic percentage with incidental impurities. These alloys evidence low crystallization temperatures (e.g. less than 515.degree. C.) and, hence, are not well suited for power magnetics applications.
European Patent. Application 0,058,269, filed May 8, 1981 discloses amorphous metal alloys consisting essentially of 12 to 16% boron, 5 to 10% silicon and 77 to 80% iron, by atom percent, with no more than incidental impurities. No disclosure is contained therein concerning alloys which exhibit, in combination, enhanced induction at elevated temperatures and long term thermal stability.
At the time that the amorphous alloys described above were discovered, they evidenced magnetic properties that were superior to then known polycrystalline alloys. Nevertheless, new applications requiring improved magnetic properties at elevated temperatures and higher thermal stability have necessitated efforts to develop additional alloy compositions.